one fret buzzes

I'm fairly new here and I have tried searching on this but I'm unable to find anything helpful.

I have a G & L Tribute L2000 (3 months old), which I'm very happy with and recently lowered my action using the great advice in this forum, but I've hit a snag.

I have set relief, saddle heights and it plays beutifully except for a buzz on the 10th fret on the D string. This is the only place it buzzes, below and above the 10th are fine as are the strings either side. It feels like it is hitting the 11th fret, there definetely seems to be slightly less clearance here than on other frets.

To get around this I have to raise the D string almost twice as high as other strings.

Is the 11th fret not level? If so why does this not happen on strings either side?

I got the same problem but with the first fret and anything above 11 on the G. I don't know what to do either. But playing lighter on the G seems to help(when I'm in the buzzing area) Try playing lighter in the "buzz spots"

I've just checked the fret with a straight edge and it does rock (and not in the good sense) over the 11th. I've also been horrified to discover I can get a 0.15 mm (0.006 inch) feeler guage between the fretboard and the flange(?) of the fret at its centre point.

There only seems to be a gap here though,the fret is square with the fretboard at both ends. Its almost like a fret with a slightly larger radius has been put in, but its difficult to compare with the other frets (I've got 4 red lines on my face to prove it ). Can this happen? If so how can I prove it? And why doesn't it affect the A string

Sorry for all the questions, and thanks for all your help in getting this far.